The crosslinking of many polymers by irradiation or by chemical means to improve their properties is a relatively new technology which has been found useful with many polymers, e.g., polyethylene, polyvinylchloride, polyoxymethylenes, polyvinylidene difluoride, etc. It is also known that the addition to such polymers of monomers which function as crosslinking promoters will have beneficial effects, e.g., as disclosed in U.S. Pat. Nos. 3,215,671 and 3,494,883. However, for some polymers only one or a few monomers function effectively in this regard and even for those polymers for which a substantial number of monomers are beneficial, there is a significant amount of selectivity and, in many cases, a drastic difference in effectiveness of monomers. Other patents disclosing such technology are U.S. Pat. Nos. 2,965,553; 3,137,674; and 3,580,829. Furthermore, it is known that the property of heat recoverability may be imparted to crosslinked polymers, e.g., according to the process of Cook et al U.S. Pat. No. 3,086,242, the disclosure of which is incorporated by reference herein.
However, as indicated in U.S. Pat. No. 3,142,629, not all polymers are susceptible to improvement by crosslinking, even with the addition of monomers which promote crosslinking in other polymers. Among polymers in wide use, polyethyleneterephthalate is perhaps the most significant polymer which has not been successfully crosslinked by irradiation. A closely related polymer, poly(tetramethyleneterephthalate) has likewise been found by applicant to realize no crosslinking when irradiated.